The project consists of a structural analysis of nerve fibers in normal and abnormal animals in order to determine the nature of the structural specialization that occur at the node of Ranvier and in the paranodal regions on either side. Freeze-fracture studies of these regions have previously shown an elaborate paranodal junctional membrane structure as well as large accumulations of particles at the node; however the significance of these specialized regions has not yet been established. These membrane structures will be investigated by means of electron microscopy of thin sections and freeze-fracture replicas and by means of histochemical stains in a variety of normal and abnormal nerve fibers in order to correlate structural differences with physiological differences in the fibers.